1. Field of the Invention
The instant invention relates generally to the field of LADAR (laser-radar) imaging technology. Specifically, the instant invention relates to a device which allows three-dimensional laser imaging of partially obscured or camouflaged targets with very high range resolution and sensitivity.
Current LADAR imaging typically comprises scanning a target with a laser and detecting the reflected photons, also referred to as a laser echo, with a photon detector such as a focal plane array. The time required for return of the laser echo from the target to the photon detector is calculated to determine the target range. The detector output signal is electronically processed to allow the definition of surface features on a three-dimensional object. Such imaging capability is valuable in situations where, for instance, a vehicle is camouflaged or obscured by foliage or in an urban environment when an imaging sensor can acquire only a limited or angular view of a target.
2. Description of the Related Art
In general, existing LADAR imaging systems include a laser source, appropriate optics in conjunction with a detector array, processing circuitry suitable for processing the detector array output into a usable form and post-processing circuitry and software capable of taking the processed detector array output and converting it into a usable format such as an image on an electronic display.
In the operation of such systems, one or more laser pulses are directed toward a desired target. The laser echoes from the target surface are received and imaged upon the detectors in a detector array using appropriate optics. Because the time of flight of the returning laser echoes will vary based on the distance between the detector array plane and the surface features from which the echoes are received, a three-dimensional image can be calculated based upon the relative echo delays.
Note that a laser echo delay of one nanosecond suggests a target surface variation of about 15 centimeters and that a laser echo delay of only 500 picoseconds translates into a target surface variation of about eight centimeters. As is evident from these short time periods, very high detector signal processing and timing circuit speeds are desirable in order to resolve target surface feature variations at a centimeter-level depth resolution. Unfortunately, existing LADAR imaging systems lack the necessary circuit speed and capacity to achieve very high (i.e., centimeter) range resolution and sensitivity.
Alternatively, conventional passive visible sensors, such as CCD video sensors, provide easily interpreted information to an observer. Nonetheless, these types of sensors are undesirable where accurate scene information in a complex video environment (i.e., camouflaged or partially obscured targets) is an important factor in the observer's decision-making.
Accordingly, a need exists for a LADAR imaging system that has the circuitry speed and density required to achieve range resolution and sensitivity necessary to define small target surface variations based on picosecond time of flight differences in laser echoes.
The instant invention addresses the aforementioned problems in prior art devices by providing a reliable, high speed, high circuit density LADAR detector system and device capable of providing range resolution and sensitivity at a centimeter level.